170 PROCEEDINGS OF THE MALACOLOGICAL SOCIETr. 



Sub-genus lo (Lea). 



? Oxytrema, llafinesque, 1819 (no type cited, description appears to 

 have been based on smooth form oi Jluviatilis) ; Fuhus (sp.), Say, 

 1823 {F. fluviatilis, Say); /o, Lea, 1832 {I. fasiformis, Lea = 

 F. fluviatiUs, Say) ; Melafusus, Swainson, 1840 (no species cited, 

 description apparently based on Jluviatilis). 



Type, Fusus fliiviatilis, Say. 



Sub-genus Pleurocera, s.s. Shell of rather large size, averaging 

 30 ram. in altitude, solid, spire elevated-conic, early whorls normally 

 smooth and rounded, adult whorls barely inflated or appressed, 

 frequently more or less nodose on the periphery, which has a tendency 

 to become sub-carinate, aperture simple, pillar straiglit and imperforate, 

 outer lip sinuate, somewhat produced and channelled below ; habitat 

 streams. 



Sub-genus lo. Shell similar to preceding but larger, averaging 

 40 ram. in altitude, moderately thin, spire elevated-conic, whorls 

 barely inflated or appressed, periphery sub-carinate and more or less 

 ornamented with nodes which increase in size and complexity with 

 the later growth tending to acquire the character of spines, imperforate, 

 outer lip deeply sinuate, and produced below into a fusiform canal ; 

 Pleurocera stage passed during adolescence; habitat in streams. 



Pleurocera includes the usually peripherally nodose, straight-pillareii, 

 more or less conical American ^felanoids, the canalled forms composing 

 the sub-genus lo. A somewhat anomalous state of affairs exists, but 

 one to be expected in the history of all genera, in that all the L)S 

 are represented by sub-species in typical Pleurocera. 



Pleukocera vekrucosa, Rafinesque. 



P. verrucosa, Rafinesque, 1820; Melania nupera, Say, 1829; Mela- 

 nopsis semigramdosa, Desliayes, 1830; 31. lima, Conrad, 1834; 

 jV. Ili/dei, Conrad, 1834; M. Floreniiana, Jjea, 1841; M. fuligi- 

 7iosa, Lea, 1841; 31. venusta, Lea, 1841; 3[. Holstonia, Lea, 

 1841 ; Lithasia dilatata, Lea, 1841. 

 Shell of moderate size, broadly conical, whorls barelj- inflated, 

 peripherv rounded, early volutions smooth, penultimate and body- 

 whorls with about five rows of tubercles, the fourth row peripheral, 

 aperture elliptical and somewhat produced below, outer lip sub-sinuate 

 and channelled at base ; habitat streams. J 



Holstou, Tennessee, and lower Ohio llivers, American Province. \ 



Pleurocera canaliculatum, Say. 



3Ielama canaliculata, Say, 1821; 31. conica, Say, 1821 (preocc.) ; 

 31. Sai/i, Wood, 1828; 31. undulata, Say, 1829; 31. exarata, 

 Menke, 1830 ; 31. ligata, Menke, 1830 ; 31. auriscalpium, jNfenke, 

 1830 ; Pleurocera quadrosa, Eaflnesque, 1831 ; 31. alvearis, 

 Conrad, 1834; 3f. anmilifera, Conrad, 1834; 31. excurtala, 

 Conrad, 1834; ]\r. prasinata, Conrad, 1834; 3f. pyrenellum, 

 Conrad, 1834; Ceriphnsia sulcata, Swainson, 1840; 3[. suh- 

 stricta, Haldeman, 1840; 31. ' nupera. Say', Say, 1840 (/;«/•«) ; 



